Discontinuities in the Dorsal Lateral Geniculate Nucleus Corresponding to the Optic Disc: A Comparative Study

t\BSTRACT A cylindrical cellular discontinuity commonly occurs in lateral geniculate layers that are Innervated by the contralateral eye. Such a disconti ­ nuity has been found In a variety of mammalian species, including carnivores, primates, a rodent and a marsupial. Electrophyslological evidence obtained from some of these species shows ulat the discontinuity corresponds to the blind spot. It is concluded that the representation of the retina within the lateral geniculate nucleus is extremely accurate, since the retinal receptor layer and the geniculate layers have corresponding holes. Two possible mechanisms that would demand slIch a discontinuity are con­ sidered. One is an Intralamlnar mechanism in which the cells In each lamlna accurately reflect the distribution of retinal receptors; the other is an lnterlam­ inar mechanism in which the representations of the homonymous hemlret:lnae are so accurately aligned that the optic disc must be represented by a cellular discontinuity.